Breathing is a physical process which involves movement of air, in and out of the lungs.
Oxygen-rich air from the external environment is taken inside the lungs and air containing more amount of carbon dioxide is expelled to the outside environment. Breathing is a continuous process that occurs throughout the life of an organism.
Inhalation and exhalation are the two steps of breathing, which occur continuously one after the other. Inhalation or inspiration is the movement of air from the outside environment to the inside of the body. Exhalation or expiration is the movement of air from the inside of the body to the outside environment.